Department: NanoEngineering
Research Institute Affiliation: Graduate Program in Materials Science and Engineering
Faculty Advisor(s): Andrew Kummel

Primary Student
Name: Tyler James Kent
Email: tjkent@ucsd.edu
Phone: 858-534-3498
Grad Year: 2015

In order for III-V semiconductors to be competitive in future MOSFETs, a high-k oxide must be deposited onto the semiconductor and exhibit a low density of interfacial traps (Dit) to minimize subthreshold swings and must be atomically flat to maintain high mobilities at large field strengths.1,2,3 Trimethylaluminum (TMA) is known to form an ordered structure on the (4x2) surface with monolayer nucleation when dosed at low temperatures.2 Recently, it has been shown that TMA exhibits superior electrical properties when deposited onto the arsenic rich (2x4) surface at elevated temperatures4. In the present study, TMA deposited onto the InGaAs(100)-(2x4) surface has been studied as a function of temperature using scanning tunneling microscopy (STM) and spectroscopy (STS) Fig.1 shows the clean surface which is comprised of single and double As dimers which are bonded to In/Ga atoms. Fig. 1 also shows a ball and stick diagram of the (2x4) surface reconstruction. A detailed discussion can be found elsewhere.3 The clean surface was dosed with 5 Langmuir of TMA at 25 oC or 280 oC and annealed at 250 oC for 30 min. Fig. 2 shows the 280 oC TMA dosed surface. The surface exhibits several different chemisorption sites and models of the different adsorbates are presented in Fig. 2. In Fig.2 (right box) aluminum atoms bridge bond in the As dimers and also insert between adjacent As dimers, clearly forming the linear subdivided row structure as seen in the image. In Fig.2 (left box) aluminum atoms bridge bond in the As dimers. With a 25 oC TMA dose, the 2x4 shows a similar surface reconstruction, shown in Fig. 3, unlike the 4x2 which has different reconstructions for high and low temperature doses. Between 240-260 oC the TMA row spacing switches from 8 to 17 for the In/Ga rich InGaAs(100)-4x2 (not shown). TMA forms an ordered monolayer on the InGaAs (2x4) surface. While the apparent coverage of the TMA on the In/Ga rich InGaAs(100)-(4x2) surface is highly dependent on dosing temperature, the structure of TMA on the As-rich InGaAs(100)-(2x4) surface is less temperature dependent making the processing conditions of the 2x4 more relaxed than on the 4x2 surface. The results are also consistent with the propensity for the Al atoms in the TMA reaction products to bridge bond to group V atoms and can be used to generate monolayer ALD nucleation templates on a variety of III-V surfaces.

Related Files:

  1. images.pdf

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